Magnetic field generator for a magnetic inductive flowmeter, method for operating same, magnetic inductive flowmeter and method for operating same

Abstract

A magnetic field generator (4) for a magnetic-inductive flowmeter (1) is shown and described, comprising a coil (7), a bridge circuit (8) with at least one current regulator (9), a voltage regulator (10), and a controller (5). The bridge circuit (8) is configured to conduct a current (i) through the coil (7) in one direction. This direction is either a first direction or a second direction, and the direction can be specified to the bridge circuit (8) by the controller (5). The current regulator (9) is configured to generate the current (i) through the coil (7) according to a set current, and the set current can be specified to the current regulator (9) by the controller (5). For normal operation of the current regulator (9), the current regulator voltage (uc) applied across the current regulator (9) is greater than or equal to a control voltage value (UC,R), and for minimum operation of the current regulator (9), the current regulator voltage (uC) is greater than a minimum voltage value (UC,M).The voltage regulator (10) is configured to generate a supply voltage (u) according to a target voltage across the bridge circuit (8), and the target voltage can be specified to the voltage regulator (10) by the controller (5). The controller (5) is configured to specify, at a first reversal point (tU,1), the first direction, a target current value (IS) as the target current, and a first target voltage value (US,1) as the target voltage, wherein the first target voltage value (US,1) is greater than a second target voltage value (US,2), and the second target voltage value (US,2) as the target voltage results in the regulated voltage value (UC,R) of the current regulator voltage (uc) in a steady state of the magnetic field generator (4). The invention solves the problem that at a switching point, the voltage across the coil (7) does not yet exhibit sufficient stability.The problem is solved by further developing the control (5) to determine a first switching time (tS,1), which is characterized by the fact that it lies after the first reversal time (tU,1), the current (i) reaches the target current value (IS) between the first reversal time (tU,1) and the first switching time (tS,1), and the current regulator voltage (uC) is greater than the minimum voltage value (UC,M) and less than the control voltage value (UC,R) at the first reversal time (tU,1), and then specifying the second target voltage value (US,2) as the target voltage at the first switching time (tS,1).

Description

[0001] The invention relates to several objects.

[0002] The invention relates to a magnetic field generator for a magnetic-inductive flowmeter. It comprises a coil, a bridge circuit with at least one current regulator, a voltage regulator, and a controller.

[0003] Another subject matter is a method for operating a magnetic field generator for a magnetic-inductive flowmeter. The magnetic field generator comprises a coil, a bridge circuit with at least one current regulator, a voltage regulator, and a controller.

[0004] Another subject matter is a magnetic-inductive flowmeter. This comprises a measuring tube, two measuring electrodes, a magnetic field generator, and a controller. The magnetic field generator comprises a coil, a bridge circuit with at least one current regulator, and a voltage regulator. The magnetic field generator is designed to generate a magnetic field in a medium flowing in the measuring tube with the coil, which induces a measuring voltage into the medium that can be tapped at the measuring electrodes. During operation of the magnetic-inductive flowmeter, a medium flows through the measuring tube.

[0005] Finally, the invention further relates to a method for operating a magnetic-inductive flowmeter. The magnetic-inductive flowmeter comprises a measuring tube, two measuring electrodes, a magnetic field generator, and a controller. The magnetic field generator comprises a coil, a bridge circuit with at least one current regulator, and a voltage regulator. A medium flows through the measuring tube.

[0006] The bridge circuit is designed to conduct a current through the coil in one direction. The bridge circuit and the coil are interconnected accordingly. The direction of the current is either a first direction or a second direction. The first direction of the current through the coil is opposite to the second direction. The direction can be specified for the bridge circuit by the controller. The bridge circuit and the controller are designed accordingly.

[0007] The magnetic field generator has two controllers: the current controller and the voltage controller. A controller regulates a controlled variable using feedback to a given reference variable, within the limits of technical feasibility. Ideally, the controlled variable is equal to the reference variable in the steady-state controller.

[0008] The current controller is designed to generate the current through the coil according to a setpoint current. Accordingly, the setpoint current is the reference variable, and the current through the coil is the controlled variable. The current controller's task is to ensure that the current corresponds to the setpoint current. The setpoint current can be specified to the current controller by the controller. The current controller and controller are designed accordingly. The current controller represents a current source for the coil.

[0009] For the current controller to be in control mode, the current controller voltage applied across the current controller is greater than or equal to a control voltage value, and for the current controller to be in minimum mode, the current controller voltage is greater than a minimum voltage value. In this case, the control voltage value is greater than the minimum voltage value. If the current controller voltage applied is greater than the minimum voltage value, then the current controller is operating in minimum mode. If the current controller voltage applied is even greater than the control voltage value, then the current controller is operating in control mode. In minimum mode, the current controller's ability to regulate the current to the target current is limited with respect to control mode.

[0010] The voltage regulator is designed to generate a supply voltage across the bridge circuit according to a setpoint voltage. In this regulator, the setpoint voltage is the reference variable, and the supply voltage is the controlled variable. The regulator's task is to ensure that the supply voltage corresponds to the setpoint voltage. The setpoint voltage can be specified to the voltage regulator by the controller. The controller and the voltage regulator are designed accordingly. The voltage regulator represents a voltage source and is electrically connected in parallel with the bridge circuit.

[0011] With respect to the subject matter of the magnetic field generator, the controller is designed to specify the first direction, a target current value as the target current and a first target voltage value as the target voltage at a first reversal time.

[0012] With regard to the subject matter of the method for operating a magnetic field generator, the controller specifies the first direction, a target current value as the target current and a first target voltage value as the target voltage in a method step at a first reversal time.

[0013] With regard to the subject matter of the magnetic-inductive flowmeter, the controller is configured to specify the first direction, a target current value, and a first target voltage value at a first reversal time. Furthermore, the controller is configured to measure a first measurement voltage applied between the measuring electrodes after a first switching time and before a second reversal time and to determine a flow rate of a medium through the measuring tube using the first measurement voltage.

[0014] With regard to the subject matter of the method for operating a magnetic-inductive flowmeter, the controller specifies the first direction, a target current value, and a first target voltage value in a method step at a first reversal time. In a further method step, the controller measures a first measuring voltage applied between the measuring electrodes after a first switching time and before a second reversal time, and a flow rate of the medium is determined using the first measuring voltage, wherein the measuring voltage in the medium is caused by a magnetic field generated by the coil in the flowing medium. The magnetic-inductive flowmeter is designed to carry out these method steps and also carries out these method steps during operation.

[0015] At a reversal point in time, such as the first reversal point in time, the bridge circuit reverses the direction of the current through the coil. If the direction is the first direction before a reversal point in time, then the direction is the second direction after the reversal point in time. At the first reversal point in time, the controller specifies the first direction as the direction of the current through the coil to the bridge circuit. Furthermore, at a reversal point in time, the controller specifies the target current value to the current regulator as the target current and the first target voltage value to the voltage regulator as the target voltage. The current regulator then regulates the current to the target current value and the voltage regulator regulates the supply voltage to the first target voltage value. The first target voltage value is greater than a second target voltage value and the second target voltage value effects the control voltage value of the current regulator voltage in a steady state of the magnetic field generator.

[0016] The current through the coil generates a magnetic field. In the steady state of the magnetic field generator, the magnetic field is sufficiently constant so that, for example, measurements using the magnetic field can be carried out with sufficient accuracy. In relation to the magnetic-inductive flowmeter and the method for operating a magnetic-inductive flowmeter, this means that the magnetic field induces a measuring voltage in a medium flowing through the measuring tube. This measuring voltage is measured by the controller using the two measuring electrodes. From the measuring voltage, the controller determines the flow of the medium through the measuring tube with sufficient accuracy.

[0017] It is known from the prior art that the controller specifies the second target voltage value as the target voltage to the voltage regulator at a switching instant, such as the first switching instant, which always occurs after a reversal instant. The switching instant is characterized by the current reaching the target current value at this instant. With coils used in practice, the problem occurs that the voltage across the coil is not yet sufficiently constant at the switching instant. As a result, the magnetic field generated by the coil is not yet sufficiently constant, and it is necessary to wait until the magnetic field is sufficiently constant. It has been recognized that one cause of the problem is eddy currents, which arise from the reversal instant onwards due to the reversal of the current through the coil. InIn this regard, EP 0 969 268 A1 and DE 10 2017 107417 A1 propose to control the coil current by regulating the voltage applied across the bridge circuit.

[0018] An alternative second setpoint voltage value can be determined that is higher than the second setpoint voltage value and usually lower than the first setpoint voltage value. If it is applied to the voltage regulator at the switching time, it solves the described problem. However, it does not meet one criterion of the sought-after solution. Namely, the alternative second setpoint voltage value results in higher power dissipation than the second setpoint voltage value because it is higher than the latter. A solution that results in higher power dissipation due to a higher second setpoint voltage value starting at the first switching time is not sought here.

[0019] A fixed alternative switching time can also be determined that occurs after the previously described switching time and, if the controller uses the alternative switching time instead of the switching time, solves the described problem. However, the alternative switching time does not meet another criterion of the sought-after solution. Namely, the fixed, longer specification of the first target voltage results in a longer duration of higher power loss than if the previously described switching time is used. A solution that results in a fixed, longer duration of higher power loss due to a temporally shifted switching time is not sought here. Instead, an adaptive solution is sought.

[0020] The object of the present invention is to provide a solution to the described problem while simultaneously fulfilling the described criteria.

[0021] The problem is solved by each of the objects of the invention.

[0022] Thus, the object is achieved by a method for operating a magnetic field generator having the features of claim 1. Accordingly, the previously described method for operating a magnetic field generator is replaced by the modified method described below with the following method steps, which are carried out by the controller: In a first method step, the first direction, a target current value as the target current and a first target voltage value as the target voltage are specified at a first reversal time, wherein the first target voltage value is greater than a second target voltage value and the second target voltage value as the target voltage effects the control voltage value of the current regulator voltage in a steady state of the magnetic field generator. In a second method step, a first switching time is determined which is distinguished by the fact that it lies after the first reversal time, the current reaches the target current value between the first reversal time and the first switching time and the current regulator voltage at the first switching time is greater than the minimum voltage value and less than the control voltage value, and the second target voltage value is specified as the target voltage at the first switching time.

[0023] In a described magnetic field generator with a coil having the problem described above, the method, in comparison to the described prior art, ensures that the voltage across the coil at the switching instant is sufficiently constant so that, for example, measurements can be carried out immediately using the magnetic field generated by the coil with sufficient accuracy.

[0024] Furthermore, using the method does not require an increase in the second target voltage value. The first switching time is determined adaptively and is usually closer to the first reversal time than in the described prior art. The method generally applies to switching times such as the first switching time and to reversal times such as the first reversal time. The method also reduces the power consumption of the magnetic field generator.

[0025] In one embodiment of the method for operating a magnetic field generator, the controller carries out the following method steps following the second method step: In a third method step, the second direction and the first target voltage value are specified as the target voltage at a second reversal time. In a fourth method step, a second switching time is determined, which is characterized in that the second switching time is after the second reversal time, the current reaches the target current value between the second reversal time and the second switching time, and the current regulator voltage at the second switching time is greater than the minimum voltage value and less than the control voltage value, and the second target voltage value is specified as the target voltage at the second switching time.

[0026] These four process steps constitute a full cycle of the process. After this, a new cycle can begin. In one embodiment, the first process step, the second process step, the third process step, and the fourth process step are performed at least twice in this order. This then constitutes two full cycles of the process.

[0027] The object is also achieved by a method for operating a magnetic-inductive flowmeter having the features of claim 4. Accordingly, the previously described method for operating a magnetic-inductive flowmeter is replaced by the modified method described below with the following method steps, which are carried out by the controller: In a first method step, the first direction, a target current value and a first target voltage value are specified at a first reversal time, wherein the first target voltage value is greater than a second target voltage value and the second target voltage value effects the control voltage value of the current regulator voltage in a steady state of the magnetic field generator. In a second method step, a first switching time is determined, which is distinguished in that it lies after the first reversal time, the current reaches the target current value between the first reversal time and the first switching time and the current regulator voltage at the first switching time is greater than the minimum voltage value and less than the control voltage value, and the second target voltage value is specified as the target voltage at the first switching time.In a third method step, after the first switching time and before a second reversal time, a first measuring voltage applied between the measuring electrodes is measured and a flow of the medium is determined using the first measuring voltage, wherein the measuring voltage in the medium is caused by a magnetic field generated by the coil in the flowing medium.

[0028] In one embodiment of the method for operating a magnetic-inductive flowmeter, the controller carries out the following process steps following the third process step: In a fourth method step, the second direction and the first target voltage value are specified as the target voltage at the second reversal time. In a fifth method step, a second switching time is determined, which is characterized in that the second switching time is after the second reversal time, the current reaches the target current value between the second reversal time and the second switching time, and the current regulator voltage at the second switching time is greater than the minimum voltage value and less than the control voltage value, and the second target voltage value is specified as the target voltage at the second switching time.In a sixth method step, after the second switching time, a second measuring voltage applied between the measuring electrodes is measured and, using the first measuring voltage and the second measuring voltage, a flow of the medium is determined, wherein the second measuring voltage in the medium is caused by a magnetic field generated by the coil in the flowing medium.

[0029] These six process steps constitute a full cycle of the process. After this, a new cycle can begin. In a further embodiment, the first process step, the second process step, the third process step, the fourth process step, the fifth process step, and the sixth process step are performed at least twice in this order. This then constitutes two full cycles of the process.

[0030] The following embodiments relate to both the method for operating a magnetic field generator and the method for operating a magnetic-inductive flowmeter.

[0031] In one of these embodiments, the controller determines the at least one switching time iteratively by gradually reducing a time interval between the at least one reversal time and the at least one switching time until the current regulator voltage at the at least one switching time is greater than the minimum voltage value and less than the control voltage value, preferably equal to the minimum voltage value.

[0032] In another of these embodiments, the control voltage value is between 2.5 V and 3.5 V, preferably 3 V.

[0033] Finally, in another of these embodiments, the minimum voltage value is between 1.5 V and 2.5 V, preferably 2 V.

[0034] In addition to the two methods described above, the problem is also solved by the devices described below.

[0035] Thus, the object is achieved by a magnetic field generator having the features of claim 10.

[0036] This is characterized in that the controller is designed to determine a first switching time, which is distinguished by the fact that it lies after the first reversal time, the current reaches the target current value between the first reversal time and the first switching time and the current regulator voltage at the first reversal time is greater than the minimum voltage value and less than the control voltage value, and then to specify the second target voltage value as the target voltage at the first switching time.

[0037] In one embodiment of the magnetic field generator, the bridge circuit has a first branch with a current regulator and a second branch with a current regulator. The current regulators are preferably designed to be switchable by the controller.

[0038] In a further embodiment, the controller is designed to carry out one of the previously described methods for operating a magnetic field generator.

[0039] Finally, the problem is also solved by a magnetic-inductive flow meter having the features of claim 12.

[0040] This is characterized in that the controller is further designed to determine the first switching time, which is distinguished by the fact that it lies after the first reversal time, the current reaches the target current value between the first reversal time and the first switching time and the current regulator voltage at the first switching time is greater than the minimum voltage value and less than the control voltage value, and then to specify the second target voltage value as the target voltage at the first switching time.

[0041] In one embodiment of the magnetic-inductive flowmeter, the bridge circuit of the magnetic field generator has a first branch with a current regulator and a second branch with a current regulator. The current regulators are preferably designed to be switchable by the controller.

[0042] In a further embodiment, the controller is designed to carry out one of the previously described methods for operating a magnetic-inductive flowmeter.

[0043] Notwithstanding the above statements, the statements relating to one subject matter of the invention shall apply accordingly to the remaining subject matters of the invention.

[0044] In detail, there are numerous possibilities for designing and developing the subject matter of the invention. Reference is made, on the one hand, to the claims subordinate to the independent claims and, on the other hand, to the following description of a preferred embodiment in conjunction with the drawing. The drawing shows Figure 1 shows an embodiment of a magnetic-inductive flowmeter in a side view, Figure 2 shows the embodiment in a sectional front view, Figure 3a shows a first embodiment of an abstracted circuit diagram of the magnetic field generator, Figure 3b shows a second embodiment of an abstracted circuit diagram of the magnetic field generator, Figure 4 shows a flow chart of an embodiment of a method for operating a magnetic-inductive flowmeter, Figure 5a shows a time profile of a supply voltage when carrying out the method, Figure 5b shows a time profile of a current regulator voltage when carrying out the method and Figure 5c shows a time profile of a current when carrying out the method.

[0045] The Figures 1 and 2 show in different views an abstract representation of essential components of an embodiment of a magnetic-inductive flowmeter 1. Figure 1shows the magnetic-inductive flowmeter 1 in a side view and Figure 2 in a sectional front view. The magnetic-inductive flowmeter 1 comprises a measuring tube 2, two measuring electrodes 3, a magnetic field generator 4, and a controller 5. The magnetic-inductive flowmeter 1 is in operation, which is why a medium 6 also flows through the measuring tube 2.

[0046] Figure 3ashows a first exemplary embodiment of an abstract circuit diagram with essential components of the magnetic field generator 4. If the magnetic field generator 4 is a stand-alone device and not part of another device—here, it is part of the magnetic-inductive flowmeter 1—then it additionally has a controller. The controller of the stand-alone magnetic field generator is then designed like the controller 5 with respect to the magnetic field generator 4. The magnetic field generator 4 has a coil 7, a bridge circuit 8 with a current regulator 9, and a voltage regulator 10. The magnetic field generator 4 is designed, with the coil 7, to generate a magnetic field 11 in the medium 6 flowing in the measuring tube 2. For this purpose, in this exemplary embodiment, the magnetic field 11 is guided by a yoke 12. The magnetic field 11 induces a tappable measuring voltage u M in the flowing medium 6 at the measuring electrodes 3.

[0047] The bridge circuit 8 is designed to conduct a current i through the coil 7 in one direction. For this purpose, it has a first switch 13, a second switch 14, a third switch 15, and a fourth switch 16. The bridge circuit 8 also has a first branch 17 and a second branch 18. The first switch 13 and the third switch 15 are located in the first branch 17, and the second switch 14 and the fourth switch 16 are located in the second branch 18. The direction of the bridge circuit 8 can be specified by the controller 5 in that the controller 5 is designed to control the switches 13 to 16. The direction is either a first direction or a second direction. The first direction is specified by the first switch 13 and the fourth switch 16 being closed and the second switch 14 and the third switch 15 being open. In this case, it is represented by a solid line with arrowheads.The second direction is determined by the fact that the first switch 13 and the fourth switch 16 are open, and the second switch 14 and the third switch 15 are closed. It is represented here by a dashed line with arrowheads. Figure 3 shows the first direction of current i. It is opposite to the second direction.

[0048] The current regulator 9 is designed to generate the current i according to a target current through the coil 7. The target current can be specified to the current regulator by the controller 5. The current regulator 9 represents a current source for the coil 7.

[0049] The current regulator 9 operates either in control mode or in minimum mode. The current regulator 9 operates in control mode when a current regulator voltage u C applied across the current regulator 9 is greater than or equal to a control voltage value UC,R, and operates in minimum mode when the current regulator voltage u C is greater than a minimum voltage value UC,M. The control voltage value UC,R is greater than the minimum voltage value UC,M. In minimum mode, the ability of the current regulator 9 to regulate the current i to a target current is limited with respect to control mode.

[0050] The voltage regulator 10 is designed to generate a supply voltage u according to a target voltage across the bridge circuit 8. The target voltage can be specified to the voltage regulator 10 by the controller 5. The voltage regulator 10 represents a voltage source and is electrically connected in parallel to the bridge circuit 8.

[0051] Figure 3bshows a second embodiment of an abstracted circuit diagram with essential components of the magnetic field generator 4. The magnetic field generator 4 has a coil 7, a bridge circuit 8 and a voltage regulator 10. The bridge circuit 8 has a first switch 13, a second switch 14, a third switch 15 and a fourth switch 16. Furthermore, the bridge circuit 8 has a first branch 17 and a second branch 18. The first switch 13 and the third switch 15 are located in the first branch 17 and the second switch 14 and the fourth switch 16 are located in the second branch 18. Furthermore, there is a current regulator 9 in the first branch 17 and a current regulator 9 in the second branch 18. The current regulator 9 in the first branch 17 can be switched by the third switch 15 and the current regulator 9 in the second branch 18 can be switched by the controller 5.In this sense, the current regulators 9 are switchable and are shown as a unit with the respective switch 15 or 16. In an alternative embodiment, the current regulator 9 itself in the first branch 17 can be switched on and off by the third switch 15, and the current regulator 9 itself in the second branch 18 can be switched on and off by the fourth switch 16.

[0052] The bridge circuit 8 is designed to conduct a current i through the coil 7 in one direction. The direction can be specified for the bridge circuit 8 by the controller 5 in that the controller 5 is designed to control the switches 13 to 16. The direction is either a first direction or a second direction. The first direction is specified here by the first switch 13 and the fourth switch 16 being closed and the second switch 14 and the third switch 15 being open. In the present case, it is represented by a solid line with arrowheads. The second direction is specified by the first switch 13 and the fourth switch 16 being open and the second switch 14 and the third switch 15 being closed. In the present case, it is represented by a dashed line with arrowheads. Figure 3b shows the first direction of current i. It is opposite to the second direction.

[0053] The current regulators 9 are designed to generate the current i according to a target current through the coil. The target current can be specified to the current regulators 9 by the controller 5. The current regulators 9 each represent a current source for the coil 7.

[0054] Otherwise, the statements regarding the first embodiment of an abstracted circuit diagram apply analogously to the second embodiment.

[0055] The controller 5 is configured to specify the first direction, a target current value IS, and a first target voltage value US,1 at a first reversal time t U,1 . The first target voltage value US,1 is greater than a second target voltage value US,2, and the second target voltage value US,2, as the target voltage, effects the control voltage value UC,R of the current regulator voltage u C in an engaged state of the magnetic field generator 4.

[0056] The controller 5 is further designed to measure a first measuring voltage value u M,1 of the measuring voltage u M present between the measuring electrodes 3 after a first switching time t S,1 and before a second reversal time t U,2 and to determine a flow of the medium 6 through the measuring tube 2 using the first measuring voltage value u M,1.

[0057] Furthermore, the controller 5 is designed to determine the first switching time t S,1 , which is characterized in that it lies after the first reversal time t U,1 , the current i reaches the target current value IS between the first reversal time and the first switching time and the current regulator voltage u C is greater than the minimum voltage value UC,M and less than the control voltage value UC,M at the first switching time, and then to specify the second target voltage value US,2 as the target voltage at the first switching time t S,1 .

[0058] Figure 4shows a flow chart of an embodiment of a method for operating the magnetic-inductive flowmeter 1. The controller 5 is designed to carry out this method and also carries it out since the magnetic-inductive flowmeter 1 is in operation.

[0059] Figure 5 shows the temporal progression of signals during the execution of the procedure. Figure 5a a time course of the supply voltage u, Figure 5b a time course of the current regulator voltage u C and Figure 5c a temporal course of the current i.

[0060] In a first method step 101, the first direction, the target current value IS, and the first target voltage value US,1 are specified at the first reversal time t U,1 . Previously, in this exemplary embodiment, the second target voltage value US,2 was specified.

[0061] In a second method step 102, the first switching time t S,1 is determined and in this the second target voltage value US,2 is specified as the target voltage.

[0062] In a third method step 103, after the first switching time t S,1 and before the second reversal time t U,2, the first measuring voltage value u M,1 of the measuring voltage u M present between the measuring electrodes 3 is measured and, using the first measuring voltage value u M,1, a flow of the medium 6 through the measuring tube 2 is determined.

[0063] In a fourth method step 104, the second direction and the first target voltage value US,1 are specified as the target voltage at the second reversal time t U,2.

[0064] In a fifth method step 105, a second switching time t S,2 is determined, which is distinguished by the fact that the second switching time t S,2 is after the second reversal time t U,2, the current i reaches the target current value IS between the second reversal time t U,2 and the second switching time t S,2 and the current regulator voltage u C at the second switching time t S,2 is greater than the minimum voltage value UC,M and less than the control voltage value UC,R, and the second target voltage value US,2 is specified as the target voltage at the second switching time t S,2.

[0065] In general, three conditions are met at a switching time t S , in this exemplary embodiment at the first switching time t S,1 and the second switching time t S,2 . Firstly, the switching time is after the immediately preceding reversal time t U . In this exemplary embodiment, there is the first reversal time t U,1 and the second reversal time t U,2 . Secondly, the current i reaches the target current value IS between the reversal time t U and the switching time t S . Thirdly, the current regulator voltage u C at the switching time t S is greater than the minimum voltage value UC,M and less than the control voltage value UC,R . The third condition is that the effect of switching the target voltage from the first target voltage value US,1 to the second target voltage value US,2 on the current regulator voltage u C has already begun to take effect.Thus, an iterative method is particularly suitable for determining the switching time t S , in which t S is varied until the three conditions are met. Switching the setpoint voltage is therefore causal for a drop in the current regulator voltage u C , in particular to a value below UC,M .

[0066] In a sixth method step 106, after the second switching time t S,2, a second measurement voltage value u M,2 of the measurement voltage u M present between the measurement electrodes 3 is measured, and a flow of the medium 6 is determined using the first measurement voltage value u M,1 and the second measurement voltage value u M,2, wherein the second measurement voltage value u M,2 in the medium 6 is also caused by the magnetic field 11 generated by the coil 7 in the flowing medium 6. Reference symbol

[0067] 1 Electromagnetic flowmeter 2 Measuring tube 3 Measuring electrodes 4 Magnetic field generator 5 Control unit 6 Medium 7 Coil 8 Bridge circuit 9 Current regulator 10 Voltage regulator 11 Magnetic field 12 Yoke 13 First switch 14 Second switch 15 Third switch 16 Fourth switch 17 First branch 18 Second branch u Supply voltage US,1 First nominal voltage value of the supply voltage US,1 Second nominal voltage value of the supply voltage u C Current regulator voltage UC,M Minimum voltage value of the current regulator voltage UC,R Control voltage value of the current regulator voltage u M Measuring voltage between the measuring electrodes u M,1 First measuring voltage value u M,2 Second measuring voltage value i Current through the coil IS Nominal current through the coil t S,1 First switching time t S,2 Second switching time t U,1 First reversal time t U,2 Second reversal time

Claims

1. Method for operating a magnetic field generator (4) for a magnetic-inductive flowmeter (1), wherein the magnetic field generator (4) comprises a coil (7), a bridge circuit (8) with at least one current regulator (9), a voltage regulator (10) and a controller (5), wherein the bridge circuit (8) is designed to direct a current (i) through the coil (7) in one direction, the direction being either a first direction or a second direction, and the bridge circuit (8) can be set to the direction by the controller (5), wherein the current regulator (9) is designed to generate the current (i) according to a target current through the coil (7) and the target current (IS) can be set in the current regulator (9) by the controller (5), wherein for a control operation of the current regulator (9), a current regulator voltage (uc) present across the current regulator (9) is greater than or equal to a control voltage value (UC,R) and for a minimum operation of the current regulator (9) the current regulator voltage (uc) is greater than a minimum voltage value (UC,M) and the control voltage value (UC,R) is greater than the minimum voltage value (UC,M), wherein the voltage regulator (10) is designed to generate a supply voltage (u) according to a target voltage across the bridge circuit (8) and the target voltage can be set in the voltage regulator (10) by the controller (5), and wherein the following method steps are performed by the controller (5): - In a first method step (101), the first direction, a target current value (IS) as target current and a first target voltage value (US,1) as target voltage are set at a first reversal time (tU,1), wherein the first target voltage value (US,1) is greater than a second target voltage value (US,2) and the second target voltage value (US,2) as target voltage effects the control voltage value (UC,R) of the current regulator voltage (uc) in a steady state of the magnetic field generator (4). - In a second method step (102), a first switching time (tS,1) is determined, which is characterized in that it lies after the first reversal time (tU,1), the current (i) between the first reversal time (tU,1) and the first switching time (tS,1) reaches the target current value (IS) and the current regulator voltage (uc) at the first switching time (tS,1) is greater than the minimum voltage value (UC,M) and less than the control voltage value (UC,R), and the second target voltage value (US,2) is set as the target voltage at the first switching time (tS,1).

2. Method according to claim 1, wherein the following method steps are performed by the controller (5) following the second method step: - In a third method step (104), the second direction and the first target voltage value (US,1) are set as target voltage at a second reversal time (tU,2). - In a fourth method step (105), a second switching time (tS,2) is determined, which is characterized in that the second switching time (tS,2) lies after the second reversal time (tU,2), the current (i) between the second reversal time (tU,2) and the second switching time (tS,2) reaches the target current value (IS) and the current regulator voltage (uc) at the second switching time (tS,2) is greater than the minimum voltage value (UC,M) and less than the control voltage value (UC,R), and the second target voltage value (US,2) is set as the target voltage at the second switching time (tS,2).

3. Method according to claim 2, wherein the first method step (101), the second method step (102), the third method step (104) and the fourth method step (105) are performed at least twice in this order.

4. Method for operating a magnetic-inductive flowmeter (1), wherein the magnetic-inductive flowmeter (1) comprises a measuring tube (2), two measuring electrodes (3), a magnetic field generator (4) and a controller (5), wherein the magnetic field generator (4) comprises a coil (7), a bridge circuit (8) with at least one current regulator (9) and a voltage regulator (10), wherein the bridge circuit (8) is designed for directing a current (i) through the coil (7) in one direction, the direction being either a first direction or a second direction, and the bridge circuit (8) can be set to the direction by the controller (5), wherein the current regulator (9) is designed to generate the current (i) according to a target current through the coil (7) and the target current can be set in the current regulator (9) by the controller (5), wherein for a control operation of the current regulator (9), a current regulator voltage (uc) present across the current regulator (9) is greater than or equal to a control voltage value (UC,R) and for a minimum operation of the current regulator (9), the current regulator voltage (uc) is greater than a minimum voltage value (UC,M) and the control voltage value (UC,R) is greater than the minimum voltage value (UC,M), wherein the voltage regulator (10) is designed to generate a supply voltage (uc) according to a target voltage across the bridge circuit (8) and the target voltage can be set in the voltage regulator (10) by the controller (5), and wherein a medium (6) is made to flow through the measuring tube (2), wherein the following method steps are performed by the controller (5): - In a first method step (101), the first direction, a target current value (IS) and a first target voltage value (US,1) are set at a first reversal time (tU,1), wherein the first target voltage value (US,1) is greater than a second target voltage value (US,2) and the second target voltage value (US,2), as target voltage, effects the control voltage value (UC,R) of the current regulator voltage (uc) in a steady state of the magnetic field generator (4). - In a second method step (102), a first switching time (tS,1) is determined, which is characterized in that it lies after the first reversal time (tU,1), the current (i) between the first reversal time (tU,1) and the first switching time (tS,1) reaches the target current value (IS) and the current regulator voltage (uc) at the first switching time (tS,1) is greater than the minimum voltage value (UC,M) and less than the control voltage value (UC,R), and the second target voltage value (US,2) is set as the target voltage at the first switching time (tS,1). - In a third method step (103), after the first switching time (tS,1) and before a second reversal time (tU,2), a first measuring voltage (uM,1) present between the measuring electrodes (3) is measured and a flow rate of the medium (6) is determined using the first measuring voltage (uM,1), wherein the first measuring voltage (uM,1) in the medium (6) is caused by a magnetic field (11) generated by the coil (7) in the flowing medium (7).

5. Method according to claim 4, wherein the following method steps are performed by the controller (5) following the third method step (103): - In a fourth method step (104), the second direction and the first target voltage value (US,1) are set as target voltage at the second reversal time (tU,2). - In a fifth method step (105), a second switching time (tS,2) is determined, which is characterized in that the second switching time (tS,2) lies after the second reversal time (tU,2), the current (i) between the second reversal time (tU,2) and the second switching time (tS,2) reaches the target current value (IS) and the current regulator voltage (uc) at the second switching time (tS,2) is greater than the minimum voltage value (UC,M) and less than the control voltage value (UC,R), and the second target voltage value (US,2) is set as the target voltage at the second switching time (tS,2). - In a sixth method step (106), a second measuring voltage (uM,2) present between the measuring electrodes (3) is measured after the second switching time (tS,2), and a flow rate of the medium (6) is determined using the first measuring voltage (uM,1) and the second measuring voltage (uM,2), wherein the second measuring voltage (uM,2) in the medium (6) is caused by a magnetic field (11) generated by the coil (7) in the flowing medium (6).

6. Method according to claim 5, wherein the first method step (101), the second method step (102), the third method step (103), the fourth method step (104), the fifth method step (105) and the sixth method step (106) are performed at least twice in this order.

7. Method according to any one of claims 1 to 6, wherein the at least one switching time (tS,1, tS,2) is determined iteratively by the controller (5), in that a time interval between the at least one reversal time (tU,1, tU,2) and the at least one switching time (tS,1, tS,2) is reduced step by step until the current regulator voltage (uc) at the at least one switching time (tS,1, tS,2) is greater than the minimum voltage value (UC,M) and less than the control voltage value (UC,R), preferably equal to the minimum voltage value (UC,M).

8. Method according to any one of claims 1 to 6, wherein the control voltage value (UC,R) is between 2.5 V and 3.5 V, preferably at 3 V.

9. Method according to any one of claims 1 to 7, wherein the minimum voltage value (UC,M) is between 1.5 V and 2.5 V, preferably at 2 V.

10. Magnetic field generator (4) for a magnetic-inductive flowmeter (1) comprising a coil (7), a bridge circuit (8) having at least a current regulator (9), a voltage regulator (10) and a controller (5) wherein the bridge circuit (8) is designed to direct a current (i) through the coil (7) in one direction, the direction being either a first direction or a second direction, and the bridge circuit (8) can be given the direction by the controller (5), wherein the current regulator (9) is designed to generate the current (i) according to a target current through the coil (7) and the target current can be set in the current regulator (9) by the controller (5), wherein for a control operation of the current regulator (9), a current regulator voltage (uc) present across the current regulator (9) is greater than or equal to a control voltage value (UC,R) and for a minimum operation of the current regulator (9), the current regulator voltage (uc) is greater than a minimum voltage value (UC,M) and the control voltage value (UC,R) is greater than the minimum voltage value (UC,M), wherein the voltage regulator (10) is designed to generate a supply voltage (u) according to a target voltage across the bridge circuit (8) and the target voltage can be set in the voltage regulator (10) by the controller (5), wherein the controller (5) is designed to set, at a first reversal time (tU,1), the first direction, a target current value (IS) as target current and a first target voltage value (US,1) as target voltage, wherein the first target voltage value (US,1) is greater than a second target voltage value (US,2) and the second target voltage value (US,2) as target voltage effects the control voltage value (Uc,R) of the current regulator voltage (uc) in a steady state of the magnetic field generator (4), wherein the controller (5) is further designed to determine a first switching time (tS,1) which is characterized in that it is after the first reversing time (tU,1), the current (i) between the first reversing time (tU,1) and the first switching time (tS,1) reaches the target current value (IS) and the current regulator voltage (uc) at the first switching time (tU,1) is greater than the minimum voltage value (UC,M) and less than the control voltage value (UC,R), and at the first switching time (tS,1) the second target voltage value (US,2) is then set as the target voltage.

11. Magnetic field generator (4) according to claim 10, characterized in that the bridge circuit (8) has a first branch (17) with a current regulator (9) and a second branch (18) with a current regulator (9), and in that preferably the current regulators (9) are designed to be switchable by the controller (5).

12. Magnetic field generator (4) according to claim 10 or 11, characterized in that the controller (5) is designed to perform a method according to any one of claims 1 to 9.

13. Magnetic-inductive flowmeter (1) with a measuring tube (2), two measuring electrodes (3), a magnetic field generator (4) and a controller (5), wherein the magnetic field generator (5) comprises a coil (7), a bridge circuit (8) with at least one current regulator (9) and a voltage regulator (10) and is designed to generate a magnetic field (11) in a medium (6) flowing in the measuring tube (2) by means of the coil (7), which magnetic field induces a measuring voltage (uM) in the medium (6) which can be tapped at the measuring electrodes (3), wherein the bridge circuit (8) is designed to direct a current (i) through the coil (7) in one direction, the direction being either a first direction or a second direction, and the bridge circuit (8) can be set to the direction by the controller (5), wherein the current regulator (9) is designed to generate the current (i) according to a target current through the coil (7) and the target current can be set in the current regulator (9) by the controller (5), wherein, for a control operation of the current regulator (9), a current regulator voltage (uc) present across the current regulator is greater than or equal to a control voltage value (UC,R) and, for a minimum operation of the current regulator (9), the current regulator voltage (uc) is greater than a minimum voltage value (UC,M) and the control voltage value (UC,R) is greater than the minimum voltage value (UC,M), wherein the voltage regulator (10) is designed to generate a supply voltage (u) according to a target voltage across the bridge circuit (8), and the target voltage can be set in the voltage regulator (10) by the controller (5), wherein the controller (5) is designed to set, at a first reversal time (tU,1), the first direction, a target current value (IS) and a first target voltage value (US,1), wherein the first target voltage value (US,1) is greater than a second target voltage value (US,2) and the second target voltage value (US,2), as target voltage, effects the control voltage value (UC,R) of the current regulator voltage (uc) in a steady state of the magnetic field generator (4), and wherein the controller (5) is further designed to measure a first measuring voltage (uM,1) present between the measuring electrodes (3) after a first switching time (tS,1) and before a second reversal time (tU,2) and to determine a flow rate of a medium (6) through the measuring tube (2) using the first measuring voltage (uM,1), wherein the controller (5) is further designed to determine the first switching time (tS,1), which is characterized in that it is after the first reversal time (tU,1), the current (i) between the first reversal time (tU,1) and the first switching time (tS,1) reaches the target current value (IS) and the current regulator voltage (uc) at the first switching time (tS,1) is greater than the minimum voltage value (UC,M) and less than the control voltage value (UC,R), and at the first switching time (tS,1) the second target voltage value (US,1) is then set as the target voltage.

14. Magnetic-inductive flowmeter (1) according to claim 12, characterized in that the magnetic field generator (4) is designed according to claim 11.

15. Magnetic-inductive flowmeter (1) according to claim 13 or 14, characterized in that the controller (5) is designed to perform a method according to any one of claims 1 to 9.

Images